I actually looked into this (albeit at relatively short notice) whilst in South America last month, but in the end just couldn’t make it work within my available time - not least because I had already squeezed in a trip to Easter Island.

There are, IIRC (?) once-weekly services to MPN from SCL (Saturday) and from GRU (Wednesday). You will struggle to find any avios availability for either of these.

Seem to recall that the GRU option is very reasonable in Y, but quite a scary price in J. If you’re keen to visit, a cash fare is almost certainly going to be your only realistic option.